A variety of techniques are available for providing visual displays of graphical or video images to a user. For example, cathode ray tube displays (“CRTs”), such as televisions and computer monitors, are very common. Such devices suffer from several limitations. Conventional CRTs are typically bulky and consume substantial amounts of power, making them undesirable for portable or head-mounted applications.
Flat panel displays, such as liquid crystal displays, plasma displays, and field emission displays, may be less bulky and consume less power. However, typical flat panel displays utilize screens that are several inches across. Such screens have limited use in head mounted applications or in applications where the display is intended to occupy only a small portion of a user's field of view.
More recently, very small displays have been developed for partial or augmented view applications and for various head-mounted applications. In augmented view applications, a portion of the display is positioned in the user's field of view and presents an image that occupies a small region 42 of the user's field of view 44, as shown in FIG. 1. The user can thus see both a displayed image 46 and background information 48.
One application of such small displays in found in dual-ended systems, i.e., systems in which images are acquired at one end and transmitted to a second end for output. For example, remote viewing systems typically utilize small detectors or cameras (such as CCD arrays) at a first end that convert images to electrical signals. Then, the electrical signals are either (a) transmitted along conductors; or (b) converted to optical data and transmitted along optical fibers to the second end. At the second end, the electrical signals or optical data are converted back to optical images by electronic or optoelectronic circuitry and a miniature display. Within the display, some form of the electronic or optoelectonic circuitry converts the electrical or optical signal to an electrical driving signal that is applied to the miniature display. The display then converts the signal to the viewable image.
Such approaches usually have several drawbacks. For example, conversion between electrical signals and optical signals typically induces image distortion and noise. Also, in typical systems, the image is reconstructed by combining light from red, green, and blue light sources (e.g., phosphors or laser diodes). Such systems can induce some form of color distortion. Moreover, electrical circuitry can be sensitive to temperature or other environmental variations and to electromagnetic fields. In many applications, temperature controllers and electrical shielding can protect the electrical circuitry. However, such controllers and shielding can impose significant weight and size limitations. In head-mounted applications, this additional weight can place stress on the wearer's neck and may also increase the difficulty of packaging.